"I think Roger is very motivated. His (end of season) was incredible; he won 15 matches in a row. I feel like Roger has the passion to win more Grand Slams," said Sampras, whose record of 14 majors has only been surpassed by the Swiss star. "I feel like when Roger is playing his best, he is still the best in the world. Not as assured as he used to be, but so aggressive as usual."

Moya, the 1998 French Open winner, echoed that sentiment.

"As long as Roger plays his best, he still has the chance to be No 1. Also, his goal is to win the Olympics (singles) which he has never touched before," said the 35-year-old Spaniard.

Although Federer regained some momentum claiming his sixth year-end championship last month, this year's three-time major titlist, Novak Djokovic, is the new leader of the elite pack. But a more mature Andy Murray and Rafael Nadal, who equaled Djokovic's feat last year, will be hot on his trail.

"It will be an interesting year to see if Novak can repeat what he did. Rafael will still be there for all the majors. Andy's got all the talent to challenge anyone," Sampras said of that trio's prospects coming into the new season.

Following Djokovic's confident performances in 2011, Moya is concerned about the compatriot Nadal's encounters with Serb world No 1.

"I'd like to see how Nadal will deal with this new situation. He somehow found a way to beat Roger when he was playing at his best, but didn't against Novak. He lost six finals in a row to him. It's a new challenge for him," said Moya, who operates a youth tennis academy in Spain.